PROJECT SUMMARY Fungal pathogens are a serious threat to human health. Invasive pulmonary aspergillosis (IPA) is a severe, life- threatening disease that occurs when Aspergillus fumigatus (AF) spores are inhaled into the respiratory tract and invade airway or lung tissue. More than 200,000 cases of invasive aspergillosis occur each year. A newly identified risk factor for IPA in critically ill patients is influenza infection. Influenza is a common respiratory illness that affects 5-20% of the population each year. Our long-term goal is to develop novel therapeutic interventions for use in clinical settings to prevent morbidity and mortality from IPA. The focus of this application is to identify cell signaling pathways that increase susceptibility to invasive fungal disease following influenza infection. We hypothesize that preceding influenza A infection inhibits leukocyte responses against secondary Aspergillus fumigatus infection through the induction of IFN?, leading to invasive pulmonary aspergillosis. Our research aims include 1) To characterize the gene regulatory architecture of leukocytes at a single cell resolution during post- influenza invasive pulmonary aspergillosis. We will perform single cell RNA sequencing on CD45+ immune cells collected from lung tissue from (1) wild-type and (2) IFN? -/- mice infected with aspergillus, influenza, and super- infected with influenza followed by aspergillus.